Process, method, and system for removing heavy metals from fluids

ABSTRACT

Trace element levels of heavy metals in crude oil are reduced by contacting the crude oil with an oxidizing agent, converting heavy metals into heavy metal cations for subsequent separation from the crude oil. At least a complexing agent is added to convert the heavy metal cations into soluble heavy metal complexes in a water phase, which can be separated from the crude oil, for a treated crude oil having reduced levels of heavy metals. In one embodiment, the complexing agent is selected from the group of metal halides, and the oxidizing agent is selected from the group of organic peracids, inorganic peracids and salts thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

None.

TECHNICAL FIELD

The invention relates generally to a process, method, and system forremoving heavy metals such as mercury and the like from hydrocarbonfluids such as crude oil.

BACKGROUND

Heavy metals such as lead, zinc, mercury, silver, arsenic and the likecan be present in trace amounts in all types of fuels such as crudeoils. The amount can range from below the analytical detection limit(0.5 μg/kg) to several thousand ppb depending on the feed source. It isdesirable to remove the trace elements of these metals from crude oils.

Various methods for removing trace metal contaminants in liquidhydrocarbon feed prior to fractional distillation have been developed.U.S. Pat. No. 4,474,896 claims the use of absorbent compositions, mainlypolysulfide based, for removal of elemental mercury from gaseous andliquid hydrocarbon streams. Absorbent beds tend to get clogged by solidparticulates in the crude, thus impeding the flow of the feed.Absorbents can also be very costly due to the large quantity needed.

U.S. Patent Application No. 2010/0078358 discloses the use of NaOCl asthe oxidizing agent for converting at least a portion of Hg(0) toHg(II). However, there is still a need to extract or convert the freemercury ions into a form that can be easily recovered and disposed. U.S.Patent Publication No. 2010/0051553 discloses the removal of mercuryfrom liquid streams such as non-aqueous liquid hydrocarbonaceous streamsupon contact with a Hg-complexing agent for mercury to form insolublecomplexes for subsequent removal.

There is still a need for improved methods for extracting trace elementsof heavy metals such as mercury and arsenic, wherein the heavy metalsform soluble metal complexes for subsequent removal from the crude bywater oil phase separation. There is still a need for improved methodsfor extracting soluble heavy metal complexes from the oilphase/interface phase into the water phase for subsequent removal.

SUMMARY OF THE INVENTION

In one aspect, the invention relates to an improved method to treat acrude oil to reduce its heavy metal concentration. In the method, awater stream consisting essentially of an oxidizing agent is added tothe crude oil to extract at least a portion of the heavy metals into thewater stream forming a waste stream. The improvement comprises adding acomplexing agent to form soluble compounds in the water stream prior toseparating the wastewater from the crude oil for a treated crude oilhaving a reduced heavy metal level.

In another aspect, the invention relates to a method for reducing atrace element of heavy metals, e.g., mercury, in a crude oil. The methodcomprises mixing into the crude oil an effective amount of an oxygencontaining compound selected from the group of oxyhalites,hydroperoxides, and organic peroxides, inorganic peracids, organicperacids, and ozone to extract the heavy metals into a water-oilemulsion; adding an effective amount of a complexing agent to thewater-oil emulsion to form soluble heavy metal complexes in the waterphase; and separating the water containing the soluble heavy metalcomplexes from the crude oil for a treated crude oil having a reducedconcentration of mercury.

DETAILED DESCRIPTION

The following terms will be used throughout the specification and willhave the following meanings unless otherwise indicated.

“Crude oil” refers to a liquid hydrocarbonaceous material.Hydrocarbonaceous material refers to a pure compound or mixtures ofcompounds containing hydrogen and carbon and optionally sulfur,nitrogen, oxygen, and other elements. Examples include crudes, syntheticcrudes, petroleum products such as gasoline, jet fuel, diesel fuel,lubricant base oil, solvents, and alcohols such as methanol and ethanol.In one embodiment, crude oil has a specific gravity of at least 0.75 ata temperature of 60° F. In another embodiment, the specific gravity isat least 0.85. In a third embodiment, the specific gravity is at least0.90.

“Heavy metals” refer to gold, silver, mercury, osmium, ruthenium,uranium, cadmium, tin, lead, and arsenic. In one embodiment, heavymetals refer to mercury.

“Trace element” refers to the amount of heavy metals in the crude oil.The amount varies depending on the crude oil source and the type ofheavy metal, for example, ranging from a few ppb to up to 30,000 ppb formercury.

“Mercury sulfide” may be used interchangeably with HgS, referring tomercurous sulfide, mercuric sulfide, or mixtures thereof. Normally,mercury sulfide is present as mercuric sulfide with a stoichiometricequivalent of one mole of sulfide ion per mole of mercury ion.

“Mercury salt” or “mercury complex” meaning a chemical compound formedby replacing all or part of hydrogen ions of an acid with one or moremercury ions.

“Oil-water” or “oil-water emulsion” or “emulsion” or “emulsions” in thecontext of oil-water (or water-oil) emulsion refers to any mixturecontaining a crude oil with water, inclusive of both oil-in-wateremulsions and water-in-oil emulsions. In one embodiment, emulsionincludes locations within an oil-water mixture in which heavy metalconcentrates, including interfaces and interface layers. In oneembodiment, emulsion is present in the initial product of oil andproduced water from the reservoir; in another embodiment, it is formedduring the mixing of the crude oil with the oxidizing agent and/or thecomplexing agent. Emulsion can be stable or unstable, such as indispersions of oil and water which can subsequently separate, as in theexample of an oil water mixture left standing for 10 minutes at roomtemperature, at least a portion (e.g., 10 vol %.) will resolve intoseparate phases. In one embodiment, the oil-water emulsion particles areof droplet sizes. In another embodiment, the emulsion particles are ofmicron or nano particle sizes. In one embodiment of oil-water emulsion,oil is present as fine droplets contained in water in the form of anemulsion, e.g., emulsified hydrocarbons, or in the form of undissolved,yet non-emulsified hydrocarbons. In another embodiment, oil-wateremulsion refers to a mixture which after mixing and allowed to standundisturbed, a portion of the mixture is resolved into separate phasesin 10 seconds. In yet another embodiment, less than 50% of the mixtureis resolved in separate phases in 10 seconds.

“Interphase,” or “interphase layer,” or “interface layer,” or “emulsionlayer” may be used interchangeably, referring to the layer in betweenthe oil and water phases, having characteristics and propertiesdifferent from the oil and water phases. In one embodiment, theinterface layer is a cloudy layer in between the water and oil phases.In another embodiment, the interface layer comprises a plurality ofaggregates of coalescence (or droplets), with the aggregates beingrandomly dispersed in either the water phase or the oil phase.

“Complexing agent” or “chelating agent” refers to a compound that iscapable of reacting with a heavy metal, e.g., mercury compounds.

“Oxidant” may be used interchangeably with “oxidizing agent,” referringto compound that oxidizes heavy metals such as mercury to form mercurycations.

“Soluble” refers to materials that dissolve in water, in conjunctionwith heavy metal removal, meaning materials that are able to dissolve inwater at concentrations comparable to the original concentration of theheavy metals in the crude oil (e.g., 1 ppb or greater).

“Halogens” refers to diatomic species from the column of the periodictable headed by fluorine, for example F₂, Cl₂, Br₂, I₂, and combinationsthereof.

“Halogen oxides” refers to molecules which combine one or more halogenatoms and oxygen, for example NaClO, ClO₂, NaClO₄.

“Organic peracids” refers to multiple-carbon organic compoundsphosphorous where the —OH in an acid group has been replaced with a —OOHgroup, e.g. a compound of the general formula RCO—OOH. Examples includebut are not limited to peracetic acid, perbenzoic acid,meta-chloroperoxybenzoic acid and combinations thereof.

“Inorganic peracids” refers to compounds of sulfur, phosphorous, orcarbon where the —OH in an acid group has been replaced with a —OOHgroup. Examples include but are not limited to peroxydiphosphoric acid,H₄P₂O₈ and peroxydisulfuric acid, H₂S₂O₈, sodium percarbonateNa₂CO₃.1.5H₂O₂, sodium peroxydisulfate Na₂S₂O₈, potassiumperoxydisulfate K₂S₂O₈, ammonium peroxydisulfate (NH₄)₂S₂O₈, andcombination thereof.

Crudes and crude blends are used interchangeably and each is intended toinclude both a single crude and blends of crudes.

The invention effectively decreases the levels of heavy metals such asmercury, lead, arsenic, etc. from crude oil. In one embodiment, thecrude oil is first brought into contact with an oxidant. In anotherembodiment, a complexing agent is added to the crude oil oxidant mixtureto extract at least a portion of the oxidized heavy metal complexes fromthe interphase to the water phase. In another embodiment for the removalof mercury, the crude oil is brought into contact with a compositioncontaining both the oxidizing agent and the complexing agent to form asoluble mercury compound. Mercury in the water phase is subsequentlyrecovered.

Oxidizing Agent: In one embodiment, the crude oil is brought intocontact with an excess amount of oxidant under suitable conditions tooxidize at least a portion of the heavy metals to cations. An organicoxidizing agent or an oxidant in an aqueous form can be used. In oneembodiment for the removal of arsenic, the oxidizing agent oxidizesreduced forms of arsenic to the 5+ oxidation state, e.g., arsine orother organic arsenic forms (soluble in hydrocarbons), arsenite (solublein water), or arsenate (soluble in water). In an embodiment for theremoval of mercury, the oxidant reacts with elemental Hg droplets,elemental Hg adsorbed on formation minerals, elemental Hg dissolved inthe crude oil, as well as mercury compounds including but not limited toHgS, HgSe, HgO, converting at least a portion of elemental mercury)(Hg°) to cations, having an oxidation state equal to or greater than 1(e.g., Hg²⁺).

In one embodiment, an effective amount of oxidant means an amountemployed to convert at least 75% of the elemental mercury to mercurycations. In another embodiment, an amount is used for a conversion of atleast 95%. In a third embodiment, at least 99%. In a fourth embodiment,an amount for at least 50% of heavy metals to be extracted from thecrude oil. In a fifth embodiment, an amount for at least 25% of heavymetal extraction from the crude oil. In yet another embodiment, theoxidant generates non-complexed ionic mercury ions from elementalmercury and complexed mercury. In one embodiment, the oxidant isselected from the group of halogens, oxides, peroxides and mixed oxides,including oxyhalites, their acids and salts thereof. In anotherembodiment, the oxidant is selected from the group of peroxides(including organic peroxides) such as hydrogen peroxide H₂O₂, sodiumperoxide, urea peroxide, alkylperoxides, cumene hydroperoxide, t-butylhydroperoxide, benzoyl peroxide, cyclohexanone peroxide, dicumylperoxide. In yet another embodiment, the oxidant is selected from thegroup of inorganic peracids such as Caro's acid (H₂SO₅) or saltsthereof, organic peracids, such as aliphatic C₁- to C₄-peracids and,optionally substituted, aromatic percarboxylic acids, peroxo salts,persulfates, peroxoborates, or sulphur peroxo-compounds substituted byfluorine, such as S₂O₆ F₂, and alkali metal peroxomonosulfate salts.Suitable oxygen-containing oxidizing agents also include other activeoxygen-containing compounds, for example ozone.

In one embodiment, the oxidizing agent is selected from the group ofsodium perborate, potassium perborate, sodium carbonate perhydrate,potassium peroxymonosulfate, sodium peroxocarbonate, sodiumperoxodicarbonate, and mixtures thereof. In another embodiment, theoxidizing agent is hydrogen peroxide in the form of an aqueous solutioncontaining 1% to 60% hydrogen peroxide (which can be subsequentlydiluted as needed). In another embodiment, the oxidizing agent is H₂O₂in the form of a stable aqueous solution having a concentration of 16 to50%. In a third embodiment, the oxidizing agent H₂O₂ is used as asolution of 1-3% concentration.

In one embodiment, the oxidant is selected from the group of elementalhalogens or halogen containing compounds, e.g., chlorine, iodine,fluorine or bromine, alkali metal salts of halogens, e.g., halides,chlorine dioxide, etc. In yet another embodiment, the compound is aniodide of a heavy metal cation. In yet another embodiment, the oxidantis selected from ammonium iodide, an alkaline metal iodide, andetheylenediamine dihydroiodide. In one embodiment, the oxidant isselected from the group of hypochlorite ions (OCL such as NaOCl, NaOCl₂,NaOCl₃, NaOCl₄, Ca(OCl)₂, NaClO₃, NaClO₂, etc.), vanadiumoxytrichloride, Fenton's reagent, hypobromite ions, chlorine dioxine,iodate IO₃ (such as potassium iodate KIO₃ and sodium iodate NaIO₃), andmixtures thereof. In one embodiment, the oxidant is selected from KMnO₄,K₂S₂O₈, K₂CrO₇, and Cl₂.

In one embodiment, the oxidant is selected from the group ofmonopersulfate, alkali salts of peroxide like calcium hydroxide, andperoxidases that are capable of oxidizing iodide.

The amount of oxidants used should be at least equal to the amount ofheavy metal to be removed on a molar basis, if not in an excess amount.In one embodiment, an effective amount (or sufficient amount) ofoxidants (and the water stream containing oxidants) is added for a molarratio of oxidant to heavy metals ranging from 1.5:1 to 30,000:1. Inanother embodiment, a sufficient amount of water containing oxidants isprovided for a molar ratio of oxidant to heavy metals ranging from 5:1to 20,000:1. In a third embodiment, an effective amount means a molarratio of oxidants to heavy metals ranging from 50:1 to 10,000:1. In afourth embodiment, an effective amount means a molar ratio ranging from100:1 to 5,000:1. In a fifth embodiment, the ratio ranges from 150:1 to500:1. The contact can be carried out at room temperature or at anelevated temperature (e.g., from 30-80° C.) for a period of time,generally ranging from seconds to 1 day. In one embodiment, the contactis between 20 seconds to 5 hours. In another embodiment, from 1 minuteto 1 hour. The volume ratio of water containing oxidants to crude oil inone embodiment ranges from 0.05:1 to 5:1. In a second embodiment, thevolume ratio ranges from 1:1 to 2:1. In a third embodiment, from 0.1:1to 1:1. In a third embodiment, the volume ratio is at least 0.5:1.

In one embodiment the oxidant selected is a hypochlorite, e.g., sodiumhypochlorite, which is commercially produced in significant quantities.The hypochlorite solution in one embodiment is acidic with a pH value ofless 4 for at least 80% removal of mercury. In another embodiment, thesolution has a pH between 2 and 3. In a third embodiment, the sodiumhypochlorite solution has a pH of less than 2. Low pH of less than 5favors the decomposition to produce OCl⁻ ions.

Complexing Agent: Depending on the selection of the oxidizing agents,some easily transform insoluble heavy metals, e.g., Hg°, to watersoluble heavy metal cations, e.g., Hg²⁺ for greater than 50% mercuryremoval with portions of the water-oil emulsion resolved into separatephases after a short period of time, e.g., less than 10 minutes. Forsome other oxidizing agents, the separation of the water and oil phasesto remove the heavy metal cations happens with the use of separationdevices, e.g., mechanical/rotating means such as a centrifuge or ahycrocyclone, for a long period of time, e.g., more than 10 minutes or20 minutes, etc.

In one embodiment, the removal of heavy metals can be enhanced with theaddition of a complexing agent to the oil-water emulsion mixture, thusalleviating the need for oil water separation device, e.g., mechanicalseparation/rotating means. Heavy metals such as arsenic, mercury, andthe like form coordination complexes with compounds including but notlimited to oxygen, sulfur, phosphorous and nitrogen containing compound.In treating the oil-water emulsion, the complexing agent forms strongcomplexes with the heavy metal cations, e.g., Hg²⁺, extracting heavymetal complexes from the oil phase and/or the interface phase of theoil-water emulsion into the water phase by forming water solublecomplexes. In one embodiment, the addition of a complexing agentessentially eliminates or reduces the volume of the oil-water emulsionlayer, and replaces with separate oil and water layers. In oneembodiment, the formation of a water layer containing heavy metalcations occurs within 15 minutes after the addition of the complexingagent. In a second embodiment, a separate water layer is formed after 10minutes. In a third embodiment, the formation of a water layercontaining soluble heavy metal cations occurs within 20 minutes of theaddition of the oxidizing agent to the crude oil. In a fourthembodiment, the formation of a water layer occurs within 15 minutes ofthe addition of the oxidizing agent to the crude oil. In a fifthembodiment, the formation is within 5 minutes.

In one embodiment for the removal of mercury, a mercury-selectivecomplexing agent has a large equilibrium binding constant fornon-complexed mercury ions and is resistant to oxidation by theoxidizing agent added to the oil-water emulsion layer (if it can beisolated), or the crude oil/oxidizing agent mixture. In one embodiment,the addition of the complexing agent allows at least 50% of the mercurycations to react with the complexing agent, forming a water solublemercury compound, e.g., mercury complexes, when it comes into contactwith the mercury cations. In another embodiment, at least 75% of themercury cations in the oil phase and/or interface phase are convertedinto water soluble complexes. In a third embodiment, at least 90%conversion. In a fourth embodiment, at least 95% of the mercury cationsare converted/extracted from the oil phase and/or interface phase intothe water phase as water soluble compounds. In yet another embodimentwith the selection of a complexing agent which also functions as areducing agent, it neutralizes excess oxidant that could make the crudeoil corrosive.

Examples of mercury-selective chelating groups include thiol groups,dithiocarbamic acid, thiocarbamic acid, thiocarbazone, cryptate,thiophene groups, thioether groups, thiazole groups, thalocyaninegroups, thiourenium groups, amino groups, polyethylene imine groups,hydrazido groups, N-thiocarbamoyl-polyalkylene polyamino groups,derivatives thereof, and mixtures thereof.

Examples of complexing agents as reducing agents include but are notlimited to hydrazines, sodium metabisulfite (Na₂S₂O₅), sodiumthiosulfate (Na₂S₂O₃) and thiourea.

In one embodiment, the complexing agent is an inorganic sulfur compoundselected from the group of sulfides, ammonium thiosulfate, alkali metalthiosulfates, alkaline earth metal thiosulfates, iron thiosulfates,alkali metal dithionites, and alkaline earth metal dithionites, andmixtures thereof. Examples of sulfides include but are not limited topotassium sulfide, alkaline earth metal sulfides, sulfides of transitionelements number 25-30, aluminum sulfides, cadmium sulfides, antimonysulfides, Group IV sulfides, and mixtures thereof.

In another embodiment, the inorganic sulfur compounds areoxygen-containing compounds such as thiosulfates and dithionites.Examples include alkali metal thiosulfates, alkaline earth metalthiosulfates, iron thiosulfates, alkali metal dithionites, and alkalineearth metal dithionites and mixtures thereof can be employed toinsolubilize soluble mercury. Suitable alkali metal thiosulfates includeammonium thiosulfate, sodium thiosulfate, potassium thiosulfate, andlithium thiosulfate. Examples of alkaline earth metal thiosulfatesinclude calcium thiosulfate and magnesium thiosulfate. Ferricthiosulfate exemplifies an iron thiosulfate which may be employed.Alkali metal dithionites include sodium dithionite and potassiumdithionite. Calcium dithionite is suitable as an alkaline earth metaldithionite complexing agent.

In another embodiment, the complexing agent is a polyamine for formingstable cationic complexes with the ions of heavy metals. Exemplarypolyamines include ethylenediamine, propylenediamine,triaminotriethylamine, diethylenetriamine, triethylenetetramine (TRIEN),tetraethylenepentamine and tetra-2-aminoethylethlenediamine. In oneembodiment, the polyamine may include carboxyl groups, hydroxyl groupsand/other substituents, as long as they do not weaken the complexforming effect of the polyamine. In one embodiment, the complexing agentis tetraethylenepentamine (TETREN), which forms a stable complex withmercury at a pH around 4.

In one embodiment, the complexing agent is selected from the group ofDEDCA (diethyl dithiocarbanic acid) in a concentration of 0.1 to 0.5M,DMPS (sodium 2,3-dimercaptopropane-1-sulfonate), DMSA(meso-2,3-dimercaptosucccinic acid), BAL (2,3-dimercapto-propanol), CDTA(1,2-cyclohexylene-dinitrilo-tetraacetic acid), DTPA (diethylenetriamine pentaacetic acid), NAC (N-acetyl L-cystiene), sodium4,5-dihydroxybenzene-1,3-disulfonate, polyaspartates;hydroxyaminocarboxylic acid (HACA); hydroxyethyliminodiacetic (HEIDA);iminodisuccinic acid (IDS); nitrilotriacetic acid (NTA),aminopolycarboxylic acids (such as ethylenediaminetetraacetic acid orEDTA), amino carboxylic acids (ethylenediaminotetraacetate,diethylenetriaminopentaacetate, nitriloacetate,hydroxyethylethylenediaminotriacetate), oxycarboxylic acids (citrate,tartrate, gluconate), and other carboxylic acids and their salt forms,phosphonates, acrylates, and acrylamides, and mixtures thereof.

In yet another embodiment, the complexing agent is a metal halide, forexample, halides selected from the group Li, Na, K, Ca, Fe, Ni, Zn andcombinations thereof. An example of a complexing agent is KI, whichcombines with mercuric iodide to form a water soluble compound havingthe formula K₂HgI₄. In another embodiment, the complexing agent isselected from nickel and ferric ions, e.g., from a salt such as FeCl₃ orNiCl₂, for forming compounds encompassing the heavy metal ions, e.g.,ferric arsenate and ferric hydroxide.

The complexing agents are employed in a sufficient amount to effectivelystabilize (forming complexes with) the soluble heavy metals in theoil-water mixture. In one embodiment, the sufficient amount is expressedas molar ratio of complexing agent to soluble mercury in the ranges of1:1 to 5,000:1. In a second embodiment from 2:1 to about 3,000:1. In athird embodiment from 5:1 to about 1,000:1. In a fourth embodiment, from20:1 to 500:1.

In one embodiment with the use of inorganic sulfur compounds ascomplexing agents, stabilizing amounts of the complexing agent employedare related, for example, to the solubility of the inorganic sulfurcompounds in water. For example, stabilizing agents which are relativelysoluble in water include alkali metal sulfides, nitrogen sulfides,alkali metal thiosulfates, ammonium thiosulfate, alkaline earth metalthiosulfates, iron thiosulfate, and alkali metal dithionites.Stabilizing amounts employed for less soluble inorganic sulfur compoundssuch as alkaline earth metal sulfides, transition metal sulfides ofelements 25 to 30, and Group IV sulfides can include molar ratios of theinorganic sulfur compound to heavy metals in the crude oil from about5:1 to about 1,000:1.

In one embodiment for the removal of heavy metals such as arsenic and/ormercury, an acidic complexing agent is employed with the addition of anacid such as HCl, for the composition to have a pH of 6 or less in oneembodiment, 5 or less in a second embodiment, and 3 or less in a thirdembodiment. In one example with the use of KI as the complexing agent, asolution mixture of KI and HCl having a pH in the range of 1.5 to 3 isemployed. In another embodiment, a solution mixture of KBr and HClhaving a pH of less than 4 is used. In a third embodiment, anHCl-thiourea solution mixture is used, with the acid concentration ofless than 5M and thioureas concentration from 0.3 to 1.4M.

Optional Reagent Treatments: In one embodiment, at least a demulsifieris added to the mixture to further chemically separate the crude oil andthe water containing the heavy metal compounds. In one embodiment, atleast a demulsifier is added at a concentration from 100 to 5,000 ppm.In another embodiment, a demulsifier is added at a concentration from100 to 1,500 ppm. In a third embodiment, the demulsifier is added alongwith pH adjustment with caustic or acid. In addition to the demulsifiertreatments, surfactants are sometimes required for resolution of solids,viscous oil-water interfaces and sludging if any.

In one embodiment, the demulsifier is a commercially availabledemulsifier selected from polyamines, polyamidoamines, polyimines,condensates of o-toluidine and formaldehyde, quaternary ammoniumcompounds and ionic surfactants. In another embodiment, the demulsifieris selected from the group of polyoxyethylene alkyl phenols, theirsulphonates and sodium sulphonates thereof. In another embodiment, thedemulsifier is a polynuclear, aromatic sulfonic acid additive.

Method for Removing/Decreasing Levels of Heavy Metals in Crude Oil: Thetrace element removal rate depends on the type of heavy metal to beremoved, the oxidant and complexing reagents employed, and in oneembodiment, the pH of the reagents. In one embodiment, an oxidant isfirst prepared or obtained. The oxidant is brought in contact with thecrude oil containing heavy metals by means known in the art. In the nextstep, at least a complexing agent is added to the crude oil-oxidantmixture, forming soluble metal complexes, thus extracting the heavymetal complexes into the aqueous phase.

Depending on the selected oxidant and/or the subsequent complexingreagent to be used, the pH of the solution can first be adjusted ormaintained by the use of a buffer to improve the removal rate. Exemplarybuffers, such as phosphate and citrate, are serviceable for a prescribedpH range. The pH can be adjusted to the alkaline range using ammoniumhydroxide, ammonium chloride, ammonium citrate, ammonium lactate,potassium hydroxide, potassium formate, sodium hydroxide, sodiumacetate, and mixtures thereof. Additionally, nitriloacetic acids can beused as buffers. The pH can be adjusted to the acidic range using acidssuch as HCl. Other exemplary acids include nitrilotriacetic acid (NTA)and ethylenediamine-N,N,N′,N′-tetraacetic acid (EDTA). In oneembodiment, the pH of the solution is maintained in a neutral range of6-8. In another embodiment, the pH of the solution is kept acidic at apH of less than 3.

The contact between the crude oil and the reagents can be at anytemperature that is sufficiently high enough for the crude oil to becompletely liquid. In one embodiment, the contact is at roomtemperature. In another embodiment, the contact is at a sufficientlyelevated temperature, e.g., at least 50° C. In one embodiment, theprocess is carried out about 20° C. to 65° C. Higher temperatures favorremoval of heavy metals in crude oil.

The contact time between the reagents and the crude oil is for asufficient amount of time for a portion of the heavy metals to beextracted from the crude oil into the water-oil emulsion, andsubsequently into the water phase. In one embodiment, the contact timeis sufficient for at least 50% of the heavy metals to be extracted fromthe crude oil into the water phase. In a third embodiment, at least 75%extraction. In a fourth embodiment, at least 90% extraction. Thesufficient amount of time is dependent on the mixing of the crude oilwith the reagents. If vigorous mixing is provided, the contact time canbe as little as 20 seconds. In one embodiment, the contact time is atleast 5 minutes. In another embodiment, the contact time is at least 30minutes. In a third embodiment, at least 1 hr. In a fourth embodiment,the contact is continuous for at least 2 hrs.

The oxidant and complexing reagents can be introduced continuously,e.g., in a water stream being brought into contact continuously with acrude oil stream, or intermittently, e.g., injection of a water streambatch-wise into operating gas or fluid pipelines. Alternatively, batchintroduction is effective for offline pipelines.

In one embodiment instead of separate or sequential feeding steps, theoxidant and complexing reagents are added to the crude oil in one singlestep, as separate compositions or as a single composition, for theoxidation of elemental dissolved heavy metals to be immediately followedby or almost simultaneously with the extraction of the oxidized heavymetals, e.g, Hg²⁺, into the water phase.

In one embodiment, the reagents are injected into the crude oil/waterstream to form highly soluble mercury complexes in the water phase, andaway from the crude oil. In one embodiment, the complexing agent canalso be used as tracers in the injection water to monitor water floodsweep efficiency or produced water returns in producing well.

After the heavy metal complexes are extracted into the water phase, thewater containing the complexes is separated from the crude oil in aphase separation device known in the art, resulting in a crude oil witha significantly reduced level of heavy metals. The soluble heavy metalcomplexes can be isolated/extracted out of the effluent and subsequentlydisposed. In one embodiment, the water phase after separation can beinjected back into the reservoir for water flooring, or reservoir watersupport as a mean of disposing the mercury that was originally in thecrude oil. In one embodiment, the water phase is disposed into orinjected back to the reservoir which produced the crude oil.

In one embodiment, instead of or in addition to the addition of at leasta complexing agent, other means are employed to enhance the resolutionof the water-oil emulsions, including but not limited to heating thecrude oil mixture (to over 50° F., and up to 185° F.), further mixingtime, further quiescent time (8 to 24 hours), pH adjustment of theoil-water emulsion, or the addition of at least a demulsifier. Inanother embodiment, a continuous electrostatic dehydrator is used tohelp with the water/oil separation. In yet another embodiment,resolution of the water-oil emulsions is enhanced with the aid of ionicliquids and/or microwave treatment.

After the oil/water separation, in one embodiment the heavy metalcomplexes are removed from water through the use of a selectiveadsorbent material, e.g., a porous resin having mercury selectivechelating groups bound thereto. In another embodiment, the heavy metalcomplexes are subsequently removed through techniques such asfiltration, coagulation, flotation, co-precipitation, ion exchange,reverse osmosis, ultra-filtration using membranes and other treatmentprocesses known in the art.

Depending on the source, the crude oil feed can have an initial heavymetal level such as mercury of at least 50 ppb. In one embodiment, theinitial level is at least 5,000 ppb. Some crude oil feed may containfrom about 2,000 to about 100,000 ppb of heavy metals such as mercury.In one embodiment with the trace element removal or reduction of heavymetals including mercury, the heavy metal level in the crude oil isreduced to 100 ppb or less. In another embodiment, the level is broughtdown to 50 ppb or less. In a third embodiment, the level is 20 ppb orless. In a fourth embodiment, the level is 10 ppb or less. In a fifthembodiment, the level is 5 ppb or less. In yet another embodiment, theremoval or reduction is at least 50% from the original level of heavymetals such as mercury or arsenic. In a fifth embodiment, at least 75%of a heavy metal is removed. In a seventh embodiment, the removal or thereduction is at least 90%.

Heavy metal levels, e.g., mercury, can be measured by conventionaltechniques known in the art, including but not limited to cold vaporatomic absorption spectroscopy (CV-AAS), cold vapor atomic fluorescencespectroscopy (CV-AFS), Gas Chromatography Combined with InductivelyCoupled Plasma Mass Spectrometry (or GC-ICP-MS with 0.1 ppb detectionlimit), Combustion Amalgamation, etc.

EXAMPLES

The following examples are given to illustrate the present invention. Itshould be understood, however, that the invention is not to be limitedto the specific conditions or details described in these examples. Inexamples calling for mercury vapor feed, a sufficient amount of mercury(e.g., one or two drops of elemental mercury in a bottle) was sparged byusing nitrogen (N₂) gas into another bottle containing white mineral oilovernight. The ppm and ppb concentrations in the tables are by weight. %Hg removal indicates the removal as a percent of amount of Hg initiallypresent.

Examples 1-11

A series of experiments are carried out, each for a different oxidant.Example 1 is a control experiment without any oxidant being used(complexing agent TETREN only at a final concentration of 30 μM). Foreach of experiments 2-11, 5 mL of mercury vapor feed was placed into a10 mL Teflon-capped centrifuge tube. Oxidant was added to make a finalconcentration as shown in Table 1. The tube was shaken vigorously forabout 2 minutes. 5 mL of distilled water was added to tube. Apre-determined volume of TETREN was added for a final concentration of30 μM. Tube was again shaken by hand vigorously for about 2 minutes,then centrifuged for 1 minute to separate oil from water. Aliquots ofthe oil and water were measured for Hg using Lumex Hg analyzer equippedwith Pyro-915+. Results of the experiments are shown in Table 1.

TABLE 1 Hg Dosage Hg in Hg in removal No. Oxidant ppm oil ppb water ppb% 1 None—control — 1027 ± 41  39 3.7 2 Iodine 1000  25 ± 15 944 98 3Sodium polysulfide 29,000 58 ± 8 1000 94 4 Sodium polysulfide 2,900 884± 19 234 13.9 5 Na persulfate 940 540 ± 15 580 47.4 Na₂S₂O₈ 6Dimethylsulfoxide 310 1050 ± 0  58 0 7 Na perborate, 610  978 ± 123 —4.8 NaBO₃ 8 Na percarbonate, 620 1065 ± 14  74 0 Na₂CO₃•1.5H₂O₂ 9 Naperiodate, NaIO₄ 840 980 ± 15 116 4.6 10 2-Iodobenzoic acid 980  892 ±103 92 13.1 11 2-Iodobenzoic acid 1960  449 ± 111 780 56.3

Examples 12-14

The same procedures in Examples 1-11 are repeated, but with Oxone™(2KHSO₅.KHSO₄.K₂SO₄) as the oxidant at different dosage level, and withdifferent complexing agents (or none) as indicated in Table 2. Theresults are listed in Table 2.

TABLE 2 Oxidant/ Complexing Dosage Hg in Hg in Hg No. Agent ppm oil ppbwater ppb removal % 12 Oxone ™/None 2420  305 ± 21 800 70.3 13Oxone ™/None 2420 246 ± 3 877 76.0 14 Oxone ™/TETREN 7260 127 ± 8 82987.6

Examples 15-25

The same procedures were repeated but with different oxidants atdifferent concentrations as shown in the table, and with TETREN as thecomplexing agent added for a final concentration at 1,500 ppm. Resultsare shown in Table 3:

TABLE 3 Dosage Hg in Hg in Hg No. Oxidant ppm oil ppb water ppb removal% 15 None—control 1150 — 5.7 16 Iodine 50  114 955 90.1 17 KBrO₃ 540 972± 83 196 15.5 18 KIO₃ 690 1083 ± 25  112 5.8 19 NaClO₃ 340 974 ± 33 16615.3 20 NaClO₂ 290 1107 ± 23  44 3.7 21 Fe₂(SO₄)₃ 1290 1111 ± 10  36 3.422 FeCl₃ 1060 906 ± 24 179 21.2 23 CuSO₄ 520 1160 ± 140 41 0 24 KMnO₄510 49 ± 5 1120 96 25 HNO₃ 200 1142 ± 103 21 0.1

Examples 26-50

The same procedures in Examples 2-11 are repeated, but with differentoxidants at different dosage levels, as well as different complexingagents at different final concentrations. Results are as indicated inTable 4.

TABLE 4 dosage ppm Complexing agent Hg in Hg No. Oxidant in oil ppm inwater oil ppb removal % 26 None—control Tetren/1500 1150 5.7 27 Iodine50 NONE 1060 7.8 28 benzoyl peroxide 50 NONE 1190 — 29 benzoyl peroxide50 Na thiosulfate/124 1020 11.3 30 benzoyl peroxide 50 Nathiosulfate/248 931 19.0 31 benzoyl peroxide 50 Na thiosulfate/496 92219.8 32 benzoyl peroxide 100 Tetren/500 1200 0 33 benzoyl peroxide 100Tetren/1500 1130 1.7 34 benzoyl peroxide 100 KI/5000 679 41.0 35 benzoylperoxide 800 KI/2000 213 81.5 36 benzoyl peroxide 800 KI/4000 29 97.5 37benzoyl peroxide 200 KI/5000 600 47.8 38 benzoyl peroxide 300 KI/5000454 60.5 39 benzoyl peroxide 400 KI/5000 354 69.2 40 benzoyl peroxide500 KI/5000 214 81.4 42 benzoyl peroxide 600 KI/5000 142 87.7 42 benzoylperoxide 700 KI/5000 62 94.6 43 t-butyl hydroperoxide 25 KI/5000 41064.3 44 t-butyl hydroperoxide 50 KI/5000 88 ± 6 92.3 45 t-butylhydroperoxide 100 KI/5000 79 93.1 46 t-butyl hydroperoxide 200 KI/500040 96.5 47 t-butyl hydroperoxide 250 KI/5000 45 96.1 48 Hydrogenperoxide 25 KI/5000 77 93.3 49 Hydrogen peroxide 50 KI/5000 32 97.2 50Hydrogen peroxide 75 KI/5000 15 98.7

Examples 51-53

50 mL of mercury vapor feed preparation containing approximately 1,100ppb Hg was added to a number of 100 mL glass tubes, then mercury levelwas measured using LUMEX mercury analyzer equipped with PYRO-915+. 50 mLof distilled water was placed in the tubes, and the mercury level wasmeasured using LUMEX mercury analyzer equipped with PYRO-915+. Apre-determined volume of 3 different oxidants (hydrogen peroxide (H₂O₂),t-butyl hydroperoxide, and cumene hydroperoxide) was added to eachreactor for a final oxidant concentration of 50 ppm. The oil-watermixture was stirred up for 1 minute. In the next step, differentcomplexing reagents (potassium iodide (KI), sodium thiosulfate(Na₂S₂O₃), TETREN, and Na₄EDTA) were added to each reactor to make afinal concentration of: 50, 500 and 5,000 ppm KI; 470 and 4,700 ppmNa₂S₂O₃; 570 and 5,700 ppm TETREN; 1,200 and 12,000 ppm Na₄EDTA. Thetubes were shaken vigorously for 1 minute. Aliquots of both oil andwater from each were analyzed for mercury. Results are presented inTable 5 showing mercury removal rate for each combination of oxidantsand reagents.

TABLE 5 KI (in ppm) Na₂S₂O₃ Tetren EDTA No. Oxidant 5,000 500 50 4,700470 5,700 570 1,200 12,000 51 50 ppm 99% 88% 30% — 24% 17% 19% na  2%H₂O₂ 52 50 ppm 40% 11% — 10% — 16% 14% 15% 12% tBHP* 53 50 ppm 35% — —16% — — — — — CHP** *tBHP: t-butyl hydroperoxide **CHP: cumenehydroperoxide

Example 54

50 mL of mercury vapor feed preparation (i.e., mineral oil) containingapproximately 1,100 ppb Hg is added to a number of 100 mL glass tubes,then mercury level is measured using LUMEX mercury analyzer equippedwith PYRO-915+. Four different samples of pre-determined volume of 5mmol/L sodium chlorite at different pH (3, 6, 9, and 11) is added toeach tube for a final oxidant concentration of 50 ppm. The pH of thesodium chlorite solution is adjusted by the addition of HCl. The mixtureis stirred up for at least 10 minutes. It is expected that high pHvalues weakens the rate of Hg° oxidation, e.g., from greater than 80%mercury removal at a pH of 3 to less than 10% at a pH of 11.

Example 55

50 mL of crude oil containing approximately 1,000 ppb Hg was added to a100 mL glass tube, then mercury level was measured using LUMEX mercuryanalyzer equipped with PYRO-915+. A pre-determined volume of 5 wt. %sodium hypochlorite solution was added to the glass tube for a finaloxidant concentration of 50 ppm. The mixture was stirred up for at least10 minutes. A cloudy oil-water emulsion was formed in the test tube,indicating that oxidation took place but it would be difficult toseparate the emulsion from the crude oil.

Example 56

50 mL of crude oil containing approximately 1,000 ppb Hg is added to a100 mL glass tube, then mercury level is measured using LUMEX mercuryanalyzer equipped with PYRO-915+. A pre-determined volume of 5 wt. %aqueous solution of FeCl₂ is added to the glass tube for a finalconcentration of 50 ppm. It expected that oxidation is to take place,but the mercury cations will remain trapped in a cloudy oil-wateremulsion and that it will be difficult to separate the emulsion layerfrom the crude oil.

Example 57

Example 56 is repeated, except that a complexing agent, e.g., KIsolution at different pH (7, 5, and 3) is added to the oil-wateremulsion, and the mixture is stirred up for at least 10 minutes. It isexpected that the acidic KI enhances the mercury removal with theformation of soluble mercury compounds which minimizes the volume of theemulsion, resulting in separate water/crude oil layers with reducedmercury level of at least 50% in the treated crude oil, or for at least50% of the mercuric compounds to be removed from the emulsion into thewater phase. It is expected that an acidic pH of 3 or less allows atleast 80% of the mercuric compounds from the interface layer into thewater layer.

Example 58

50 mL of mercury vapor feed preparation containing approximately 1,100ppb Hg is added to a number of 100 mL glass tubes, then mercury level ismeasured using LUMEX mercury analyzer equipped with PYRO-915+. Apre-determined volume of hydrogen peroxide (H₂O₂) is added to each tubefor a final oxidant concentration of 50 ppm. The oil-water mixture isstirred up for 1 minute. Thiourea is added to 200 cm³ of HCl 2M toproduce a concentration of 110g/l. The mixture is added to the glasstube and stirred up for at least 60 minutes. Mercury extraction into thewater phase is expected to be as comparable to using KI as a complexingagent, of up to 99%, with the advantage that thioureas as a complexingagent is more economical than KI.

Example 59

To four glass bottles, the following is added: 1) a control sample of 40g crude oil containing approximately 20,000 ppb Hg, 2) 40 g crude oiland 40 g deionized water, 3) 40 g crude oil and 40 g of 5.6-6.0% sodiumhypochlorite (bleach) solution; 4) 40 g crude oil and 40 g of 5.6-6.0%sodium hypochlorite (bleach) solution. The samples are shaken for 2minutes, forming oil-water emulsion in samples 2-4. Samples 1-3 arecentrifuged at 90° C. and 3500 RPM for 20 minutes, effecting a water-oilseparation. Sample 4 is not centrifuged and left as is—still showingoil-water emulsion even after 20 minutes.

The oil and water phases from the samples 1-3 are analyzed for mercury.It is expected that samples 1-2 show no mercury removal with the mercurystill remaining in the crude oil. Sample 3 (using centrifuge tofacilitate oil water separation) is expected to show a mercury removalrate of at least 70%. Sample 4 cannot be easily analyzed due to theoil-water emulsion.

Example 60

Sample 4 with oil-water emulsion is stirred up for 1 minute. Potassiumiodide (KI) is added to the sample for a final concentration of 5,000ppm KI. The glass bottle is shaken vigorously for 1 minute. Aliquots ofboth oil and water from each are analyzed for mercury. The sample isexpected to show a mercury removal rate of at least 70% (as with sample3), and without the need for centrifuge

For the purposes of this specification and appended claims, unlessotherwise indicated, all numbers expressing quantities, percentages orproportions, and other numerical values used in the specification andclaims, are to be understood as being modified in all instances by theterm “about.” Accordingly, unless indicated to the contrary, thenumerical parameters set forth in the following specification andattached claims are approximations that can vary depending upon thedesired properties sought to be obtained by the present invention. It isnoted that, as used in this specification and the appended claims, thesingular forms “a,” “an,” and “the,” include plural references unlessexpressly and unequivocally limited to one referent. As used herein, theterm “include” and its grammatical variants are intended to benon-limiting, such that recitation of items in a list is not to theexclusion of other like items that can be substituted or added to thelisted items.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to make and use the invention. The patentable scope is defined bythe claims, and can include other examples that occur to those skilledin the art. Such other examples are intended to be within the scope ofthe claims if they have structural elements that do not differ from theliteral language of the claims, or if they include equivalent structuralelements with insubstantial differences from the literal languages ofthe claims. All citations referred herein are expressly incorporatedherein by reference.

1. A method for reducing a trace element of heavy metals in a crude oil,comprising: mixing into the crude oil an effective amount of at least anoxidizing agent selected from the group of oxyhalites, hydroperoxides,organic peroxides, inorganic peracids and salts thereof, organicperacids and salts thereof, ozone and combinations thereof to extract atleast a portion of the heavy metals into a water-oil emulsion; adding aneffective amount of a complexing agent to convert the extracted heavymetals to soluble heavy metal compounds in a water phase; and separatingthe water phase containing the soluble heavy metal compounds from thecrude oil for a treated crude oil having a reduced concentration ofheavy metals.
 2. The method of claim 1, for treating a crude oil havinga specific gravity of at least 0.75 at 60° F.
 3. The method of claim 1,wherein the complexing agent is a metal halide.
 4. The method of claim1, wherein the oxidizing agent is an oxygen containing compound selectedfrom the group of oxyhalites, hydroperoxides, and organic peroxides,inorganic peracids and salts thereof, organic peracids and saltsthereof, ozone, and combinations thereof.
 5. The method of claim 4,wherein the oxidizing agent is selected from the group of sodiumperborate, potassium perborate, sodium carbonate perhydrate, potassiumperoxymonosulfate, sodium peroxocarbonate, sodium peroxodicarbonate, andmixtures thereof.
 6. The method of claim 4, wherein the oxidizing agentis an oxyhalite.
 7. The method of claim 1, wherein the heavy metalscomprise mercury.
 8. The method of claim 7, wherein the oxidizing agentis NaOCl.
 9. The method of claim 1, wherein the oxidizing agent isferrous halide.
 10. The method of claim 11, wherein the oxidizing agentis FeCl₂.
 11. The method of claim 1, wherein the addition of thecomplexing agent occurs either before, simultaneously with, or after theaddition of the oxidizing agent to the crude oil.
 12. The method ofclaim 1, wherein the addition of the complexing agent occurs after theaddition of the oxidizing agent to the crude oil.
 13. The method ofclaim 1, wherein the addition of the complexing agent converts at least50 mole % of the extracted heavy metals to soluble heavy metalcompounds.
 14. The method of claim 13, wherein the addition of thecomplexing agent converts at least 80 mole % of the extracted heavymetals to soluble heavy metal compounds.
 15. The method of claim 1,wherein the complexing agent is selected from the group ofethylenediamine, propylenediamine, triaminotriethylamine,diethylenetriamine, triethylenetetramine (TRIEN),tetra-2-aminoethylethlenediamine, tetraethylenepentamine (TETREN),sulfides, ammonium thiosulfate, alkali metal thiosulfates, alkalineearth metal thiosulfates, iron thiosulfates, alkali metal dithionites,and alkaline earth metal dithionites, and mixtures thereof.
 16. Themethod of claim 1, wherein the complexing agent is KI.
 17. The method ofclaim 1, wherein the treated crude oil contains less than 50 ppb heavymetals.
 18. The method of claim 1, wherein the separation of the waterphase containing soluble heavy metal compounds from the crude oil for atreated crude oil having a reduced concentration of heavy metals iswithout using mechanical or rotating means.
 19. The method of claim 1,wherein the formation of soluble metal complexes in a water phase occurs15 minutes after the addition of the complexing agent.
 20. The method ofclaim 1, wherein at least 50% of the heavy metal are extracted andconverted to soluble heavy metal complexes in the water phase.
 21. Amethod for reducing a trace element of mercury in a crude oil,comprising: mixing into the crude oil a water stream containing aneffective amount of an oxidizing agent selected from the group of sodiumperborate, potassium perborate, sodium carbonate perhydrate, potassiumperoxymonosulfate, sodium peroxocarbonate, sodium peroxodicarbonate, andmixtures thereof; adding an effective amount of a metal halide to formsoluble mercury compounds in a water phase; and separating the waterphase containing the soluble mercury compounds from the crude oil for atreated crude oil having a reduced concentration of mercury.
 22. Themethod of claim 23, wherein the complexing agent is KI.
 23. The methodof claim 24, wherein the oxidizing agent is potassium peroxymonosulfate.24. A method for reducing a trace element of heavy metals in a crudeoil, comprising: adding to the crude oil a water stream containing anoxidizing agent to extract at least a portion of the heavy metals into awater-oil emulsion; adding an effective amount of a complexing agent toconvert the extracted heavy metals to soluble heavy metal compounds in awater phase; and separating the water phase containing the solublemercury compounds from the crude oil for a treated crude oil having areduced concentration of mercury.
 25. The method of claim 24, whereinthe oxidizing agent is selected from the group of elemental halogens,halogen containing compounds, oxyhalites, hydroperoxides, and organicperoxides, inorganic peracids, organic peracids, ozone, and mixturesthereof.
 26. The method of claim 25, wherein the oxidizing agent isselected from the group of sodium perborate, potassium perborate, sodiumcarbonate perhydrate, potassium peroxymonosulfate, sodiumperoxocarbonate, sodium peroxodicarbonate, and mixtures thereof.
 27. Themethod of claim 24, wherein the complexing agent is a metal halideselected frown the group of K, Li, Na, Ca, Fe, Ni, and Zn.
 28. Themethod of claim 24, wherein the complexing agent is selected from thegroup of sulfides, ammonium thiosulfate, alkali metal thiosulfates,alkaline earth metal thiosulfates, iron thiosulfates, alkali metaldithionites, alkaline earth metal dithionites, alkali metalperoxomonosulfate compounds, and mixtures thereof.